How can a city like Denver or Atlanta have an airport that handles far more traffic than JFK in New York? You?

could take both, Atlanta and Denver and multiply them by 10, and they still would be nowhere near the size and population of New York. So, how in world did they end up with larger airports?! Only in America! In most of the rest of the world (especially Europe) the size of the airport is, usually, related to the size of its city. Rome, being the largest city in Italy has the largest airport. Ditto for London, Paris, Madrid, etc. Shouldn't JFK have the the most dramatically huge airport in America, by far?

The size of the served region is not the best indicator for the amount of travelers at a specific airport. Most airlines have several major airports that they fly to. They are called HUBS. So if you want to travel from point a to point b, it is very likely that you have to fly to a major hub first, from where the connecting flight leads you to your destination. For example, most flights from Japan land in Los Angeles or Seattle first, before connecting flights get you to Midwest or East Coast cities.

Delta & Airtran are both based out of Atlanta which means that most flights in that quadrant of the United States will involve a layover there. The fact that Delta, a major international carrier, has a hub there also means that it will be the point of entry for most foreign flights.

Another important note is that Atlanta, a metropolitan area of 4+ million people only has ONE airport while New York has JFK, LGA, EWR. If you combine all the NYC airports it would probably rival ATL but they are distributed so the numbers are less impressive.